1. Field
This document relates to an image display device and a driving method thereof for improving picture quality.
2. Related Art
With the advancement of various image processing techniques, image display systems capable of selectively displaying 2D images 3D images are developed.
Methods of generating 3D images are divided into a stereoscopic technique and an autostereoscopic technique.
The stereoscopic technique uses disparity images of left and right eyes, which have high 3D effect, and includes a stereoscopic method and an autostereoscopic method which are practically used. The autostereoscopic method provides an optical plate such as a parallax barrier for separating optical axes of left and right disparity images from each other before or behind a display screen. The stereoscopic method displays left and right disparity images having different polarization directions on a liquid crystal display panel and generates 3D images by using polarizing glasses or liquid crystal shutter glasses.
The stereoscopic method is divided into a first polarizing filter method using a pattern retarder film and polarizing glasses, a second polarizing filter method using a switching liquid crystal layer and polarizing glasses, and a liquid crystal shutter glasses method. In the first and second polarizing filter methods, 3D images have low transmissivity due to the pattern retarder film or the switching liquid crystal layer, which is arranged on a liquid crystal display panel to function as a polarizing filter.
The liquid crystal shutter glasses method alternately displays left-eye and right-eye images on a display frame by frame and opens/closes left-eye and right-eye shutters of liquid crystal shutter glasses in synchronization with the display timing to generate a 3D image. The liquid crystal shutter glasses open only the left-eye shutter for an nth frame period in which a left-eye image is displayed and open only the right-eye shutter for an (n+1)th frame period in which a right-eye image is displayed to generate binocular disparity in a time division manner.
In the above image display systems, a liquid crystal display (LCD) is widely used as an image display device. The LCD, a hold type display device, holds data charged in a previous frame right before new data is written because of maintenance characteristic of liquid crystal. The response of liquid crystal is delayed according to data writing. The response delay of liquid crystal causes motion blurring when a left-eye image is changed to a right-eye image or when a right-eye image is changed to a left-eye image while the LCD generates a 3D image to result in 3D crosstalk in the form of a ghost.
Various methods for improving the response characteristic of liquid crystal for 2D images are known. Over driving control (ODC) compares previous frame data and current frame data to each other, detects a data variation according to the comparison result, reads a compensation value corresponding to the data variation from a memory and modulates input data with the read compensation value. Referring to FIG. 1, the ODC modulates the current frame data into “223” larger than “191” when the previous frame data is “127” and the current frame data is “191” and modulates the current frame data into “31” smaller than “63” when the previous frame data is “191” and the current frame data is “63” so as to improve the response characteristic of liquid crystal. Black data insertion (BDI) inserts a black frame between neighboring frames to improve motion blurring to thereby enhance the response characteristic of liquid crystal.
To improve the 3D crosstalk, it is considered to apply the above-described methods for improving the response characteristic of liquid crystal to image display devices, as shown in FIG. 2. In FIG. 2, “L” represents a left-eye data frame displaying a left-eye image, “R” represents a right-eye data frame displaying a right-eye image, and “B” denotes a black data frame displaying a black image.
However, the black data frame B is located before the left-eye data frame L or right-eye data frame R in FIG. 2, and thus it is difficult to effectively improve the 3D crosstalk using the existing ODC logic and compensation values. For example, when the left-eye data frame L, the black data frame B, and the right-eye data frame R respectively correspond to the (N−2)th frame F(n−2), the (n−1)th frame F(n−1), and the nth frame F(N), a variation in the luminance of the nth frame F(n) to which the ODC is applied is generated between a case (A) where target gray-scale values of the frames are “255”, “0” and “175” and a case (B) where the target gray-scale values of the frames are “0”, “0” and “175”. This is because liquid crystal rises such that the initial luminance Di of the nth frame F(n) in the case (A) is different from the initial luminance Di of the nth frame F(n) in the case (B) due to a response delay of liquid crystal even when the same compensation value (that is, “191”) is applied with reference to the target gray-scale value “0” of the (n−1)th frame F(n−1) in order to achieve the target gray-scale value “175” of the nth frame F(n). The response of liquid crystal is proportional to a gray-scale difference between the (n−2)th frame F(n−2) and the (n−1)th frame F(n−1), and thus the initial luminance Di in the case (A) is higher than the initial luminance Di in the case (B).
To effectively remove the 3D crosstalk without causing the aforementioned luminance variation when 3D images are generated, gray-scale information about the (n−2)th frame F(n−2) has to be considered when data of the nth frame F(n) is ODC-modulated in relation to the (n−1)th frame F(−1).